300 Dr. Herschel's Experiments on the Solar, and 



but allow, that certain rays, whether it be those that shine or not, 

 issue from an ignited poker, which are subject to the regular 

 laws of reflection, and have a power of heating bodies. 



5th Experiment. Reflection of the Heat of a Coal Fire by a plain 



Mirror. 



I placed a small speculum, such as I use with my 7-feet re- 

 flectors, upon a stand, and so as to make an angle of 45 degrees 

 with the front of it.* This was afterwards to face the fire in my 

 parlour chimney, and would make the same angle with the bars 

 of the grate. At a distance of 3-^ inches from the speculum, on 

 the reflecting side of it, was placed the thermometer No. 1 ; and 

 close by it, but out of the reach of the reflected rays, the ther- 

 mometer No. 4. The whole was guarded in front, against the 

 influence of the fire, by an oaken board 1^ inch thick, which 

 had a circular opening of 1^ inch diameter, opposite the 

 situation of the plain mirror, in order to permit the fire to shine 

 upon it. The thermometers were divided from the mirror by a 

 wooden partition, which also had an opening in it, that the re- 

 flected rays might come from the mirror to No. 1, while No. 4 

 remained screened from their influence. On exposing this 

 apparatus to the fire, I had the following result. 





No. 1. 





No. 4, 



0' 



60 





60 



1 



62 





60 



2 



64 





60 



3 



66 





60 



4 



66 





60 



5 



6 7 





6oi 





* See Plate XII. 



Fig- 3- 





